1. Field of the Technology
The present application relates generally to mobile stations and network selection methods employed thereby.
2. Description of the Related Art
A mobile communication device, such as a cellular mobile station, may be capable of making and receiving telephone calls and/or sending and receiving data over a wireless communication network. Before it is able to do this, the mobile station selects and registers with one of a plurality of communication networks which are available within its geographic coverage area. After registering with the selected network, the mobile station operates in an idle mode where it “camps-on” a particular wireless communication channel of the network to monitor for calls or messages. “Network selection” is the particular process performed by the mobile station for selecting the one communication network through which to register and operate.
Cellular telephony operation and network selection schemes are documented in standards specifications that govern the behavior of cellular mobile stations and associated systems. One well-known cellular standard is the Global System for Mobile Communications (GSM) standard. GSM 03.22/European Technical Standards Institute (ETSI) Technical Specification (TS) 100 930, Technical Specification (TS) 23.122 from the 3rd Generation Partnership Project (3GPP), and other related standards documents describe the many details of cellular operation and network selection. These documents describe how a mobile station behaves as it moves and roams between various regions and countries to maintain coverage with networks (referred to as Public Land Mobile Networks or PLMNs), primarily for the purpose of providing continuous telephone service.
Traditionally, a mobile station performs network selection by initially scanning to identify all available communication networks within its surrounding coverage area. Each network is identified by a unique Mobile Country Code (MCC) and Mobile Network Code (MNC) pair. If the Home Public Land Mobile Network (HPLMN) or “home network” of the mobile station is available, the mobile station will ordinarily select and operate with the home network. If the HPLMN is unavailable, the mobile station will ordinarily select and operate with the communication network having the highest priority in a preferred network list stored in memory of the mobile station. There may be several preferred network lists, commonly referred to as Preferred PLMN lists (PPLMN lists), stored on a Subscriber Identity Module (SIM) card of the mobile station. For example, the PPLMN lists may include a user-controlled PPLMN (U-PPLMN) list and an operator-controlled PPLMN (O-PPLMN) list.
The above-described network selection method is commonly referred to as an “automatic” network selection method. As an alternative to this automatic selection method, an end-user of the mobile station may be provided with the ability to manually select from a plurality of listed available networks which are visibly displayed on the mobile device. This conventional network selection method may be referred to as a “manual” network selection method.
Mobile data communication devices which are known to facilitate services such as wireless e-mail, Internet access, as well as voice telephony, are becoming more and more popular. In addition to operating in accordance with GSM for voice telephony, these mobile stations may operate in accordance with General Packet Radio Service (GPRS). GPRS is a packet-based communication protocol for mobile stations that allows data packets to be sent and received through a wireless communication network. In order to receive data services through a GPRS-capable network, the mobile station first performs a “GPRS attach” and provides its identification code and availability to the wireless network. For GSM/GPRS, this code could include both the International Mobile Subscriber Identity (IMSI) or Packet Temporary Mobile Subscriber Identity (PTMSI), which identify a communication network account or subscription, and a Mobile Station ISDN/PSTN Number MSISDN, which identifies the mobile station user or subscriber. After attaching to the network, the mobile station will attempt to establish a “Packet Data Protocol (PDP) context”. The PDP context targets an access point name (APN) and home service of the mobile station. The POP context also allocates an IP address for the mobile station so that IP packets can be communicated.
In order to operate fully as intended, these “data-capable” mobile stations must have the appropriate communication services supported and made available by the communication network that it is registered with. Ideally, all communication networks around the world should be connected through roaming agreements, and support and make available all the different types of communication services that a mobile station is capable of providing. In practice, however, some communication networks do not have or cannot make a particular communication service (e.g. a data communication service) available to a mobile station. This problem may be partially mitigated in a given coverage area, as there may be several communication networks from which the mobile station may select.
Traditional network selection techniques for GSM services, however, do not take into consideration the availability of other services (e.g. data communication services) in its decision-making process. That is, traditional network selection techniques are voice-service-centric. As a result, an inadequate communication network may be selected by such mobile stations. For example, a mobile station may select a communication network that can provide an acceptable voice service but not a data service, even though another adequate and available network could provide both the voice and the data service. Such traditional operation is undesirable, especially for mobile stations that are primarily intended to provide the end-user with a data communication service (e.g. portable e-mail devices). In particular, a GPRS/GSM-capable network is more preferably for these mobile stations than are GSM-only networks.
A better and non-traditional network selection technique for these mobile stations would involve prioritizing the selection of data-capable communication networks (e.g. GPRS) over voice-only networks (e.g. GSM). In such a procedure, the mobile station may have to determine whether or not the data service is actually made available by the communication network. More particularly, the mobile station makes a request for a data service which may be accepted or denied by the network. When data service is denied, the mobile station receives different “reject cause codes” from the network which are associated with different reasons for service denial. Depending on the reject code, the mobile station may have to wait until it may request the data service again, a timer expires, the network changes, or the user cycles the power (off & on) of the mobile device. If the end user is not viewing the display of the mobile station (e.g. the mobile station is carried in a holster), the user will not be aware of the data service unavailability and may not receive important push data in a timely fashion (e.g. pushed e-mail messages).
In a related problem, if the GPRS attach or a Routing Area Update (PRAU) attempt is not successful with the network (e.g. no network response, or the receipt of a rejection code), the mobile station consecutively reattempts for up to five (5) times. If the GPRS attach or RAU attempt counter is greater than or equal to five, the mobile station must place itself into a “GPRS Deregistered” state and start a timer designated as “timer 3302”. Timer 3302 is set to a value taken from GSM timer 3212, which is a periodic location update timer. See e.g. 3GPP specification 4.08 Release 1997. From 3GPP specification 24.08 Release 1999, the default value of T3302 is 12 minutes if one is not provided by the network. Thus, the mobile station ordinarily receives the value for timer 3212 over-the-air by the network or, if one is not provided by the network, utilizes a default value. If provided over-the-air by the network, the timer may be set to up to four (4) hours. The mobile station is not able to attempt for GPRS services again until this timer 3302 expires. As apparent, this may cause substantial data delays (e.g. delays in receiving “pushed” e-mail messages).
Accordingly, there is a resulting need for network selection methods and apparatus that overcome the deficiencies of the prior art.